Just a question: Who gives this argument for direct reference? I haven't seen it in Kripke or any of the other big names in Phil of Lang. Just curious where you got this specific argument?The four arguments are listed here. The argument referred to was the first of the four arguments, namely that that a proper name does not signify something that is repeatable, therefore does not signify a property. Therefore it signifies an object. Where did the argument come from? It is loosely based on Kripkean arguments against the view that proper names are non-rigid designators. I.e. I am assuming that 'non-repeatability', which Kripke does not invoke, is close enough to his notion of 'rigidity'.
The second and third arguments are closer to the early modern and medieval discussions of proper names. The fourth argument (that truth-conditional semantics rests on the assumption that the conditions for the truth of a sentence give the sentence’s meaning or significance) was taken almost verbatim from Teresa Marques' "On an argument of Segal’s against singular object-dependent thoughts" (Disputatio, volume II, no. 21, pp. 19-37) although her argument in turn owes much to John McDowell and Gareth Evans.
I haven't replied to the fourth argument yet, due to distractions about global warming and other distracting things.